1. Field of the Invention
The present invention relates to a method of forming an image and an image forming apparatus which method and apparatus use printing agents (for example, inks) for the three primary colors of subtractive color mixture and a printing agent for a particular color having a hue different from those of the three primary colors, and specifically, to a method of forming an image, an image forming apparatus, and a program all of which enable image formation which is excellent in color reproducibility and weatherability.
2. Description of the Related Art
With the recent popularization of information processing equipment such as word processors, personal computers, and facsimile machines, printing apparatuses have been rapidly developed and popularized as image forming terminals that print texts, images, and the like on printing media. The printing apparatuses are based on various systems. Among them, a system is common which forms texts or images by applying printing agents to printing media. The principal printing apparatus for personal use is an ink jet printing apparatus that eject inks as printing agents from ejection openings to execute printing on printing media such as paper, cloths, plastic sheets, or OHP sheets. The ink jet printing apparatus has very excellent characteristics; it is based on a low-noise non-impact printing system, can perform a dense and fast printing operation and deal easily with color printing, and is inexpensive,
The ink jet printing apparatus reproduces colors on the basis of subtractive color mixture basically using the three primary colors for printing, yellow, magenta, and cyan. For example, an image in an orange or read area can be formed by mixing yellow with magenta, an image in a green area can be formed by mixing yellow with cyan, and an image in a blue or violet area can be formed by mixing magenta with cyan. Moreover, contrast may be improved and neutral colors may be stably reproduced by executing a UCR process of using a black ink in addition to inks for the three primary colors, extracting a black component K from data Y, M, and C on yellow, magenta, and cyan to partly replace the black with this component, and removing an amount of color components C, M, and Y corresponding to the replaced part of the black. In this case, an image is formed using printing agents (inks) for the respective colors, by converting the three color components R, G, and B of the input image data into data Y, M, and C on yellow, magenta, and cyan and into data K on black.
Further, with recent rapid popularization of color ink jet printing apparatuses, image quality has been desired to be further improved. In particular, vivid output images are desired which are obtained by expanding color areas that can be reproduced by printing apparatuses. In contrast, for a color area that can be reproduced by only one of the three colors yellow, magenta, and cyan, a color reproduced area can be expanded by improving the color developing characteristics of color materials for the individual printing agents (inks) or the concentrations of the color materials. However, for a color area with a particularly high chroma within a red, green, or blue area formed using printing agents for two or more colors, the reproducible color area is limited if only three colors, that is, yellow, magenta, and cyan, or only four colors, that is, these three colors plus black are used. Consequently, more vivid color reproductions are difficult.
In connection with the expansion of the color reproduction area, Japanese Patent Application Laid-open No. 6-57654(1994) discloses a method of forming an image by using not only printing agents for the four basic colors yellow, magenta, cyan, and black but also a printing agent for a particular color that is a high-chroma color different from the three primary colors of subtractive color mixture, that is, red (orange), green, and blue (violet).
Further, Japanese Patent Application Laid-open No. 2001-138552 discloses a method of forming an image by using printing agents for the four basic colors yellow, magenta, cyan, and black, and by adding printing agents for light cyan and light magenta having lower color material densities than cyan and magenta, respectively, and particular colors including printing agents for orange and green. Both patents use particular color with high chroma in order to reproduce vivid colors that cannot be reproduced using only yellow, magenta, cyan, and black.